The parts alone to do it properly are several hundred dollars - the inlet box is around $60, 25 feet of 10/3 cable is $100 (obviously more for longer - wiring has gotten really expensive the past few years), circuit breaker $20, interlock kit is $150 (https://interlockkit.com/product/square-d-kit-k-5010-125-200...). Plus permit and inspection ($150 is the cheapest permit in my town). That's already $480 and you haven't even talked to the electrician yet.

If you get lucky and find an inexpensive electrician AND the inlet you want to install is located very close to the panel (minimal drilling, short wire, etc.), you can probably get it done for less than $1000, but probably not a whole lot less.